The present application relates to a seat belt retractor, for retracting a seat belt such that the seat belt can be freely withdrawn and wound, in a seat belt apparatus installed in a vehicle.
More particularly, the present application relates to a seat belt retractor which comprises a seat belt load limiting mechanism for absorbing an occupant's kinetic energy to limit a load on a seat belt and prevent seat belt withdrawal in the event of an emergency such as a sudden stop or vehicle collision.
Traditionally, a seat belt apparatus installed in a vehicle, such as an automobile, restrains occupants in the event of an emergency situation as mentioned above. Such an apparatus is provided with a seat belt retractor that is used to coil the seat belt. The seat belt remains wound onto a spool when not in use and is withdrawn from the spool when the seat belt apparatus is required, i.e., to be worn by a vehicle occupant. The seat belt retractor has a locking mechanism which is activated in the event of an emergency to prevent the spool from rotating in the direction of seat belt withdrawal, preventing the retraction of the seat belt, and thereby securely restraining the occupant in the event of an emergency situation.
In the event of such an emergency situation, an occupant can be forced in a forward direction by inertia due to the deceleration of the vehicle thereby applying a load to the seat belt caused by the kinetic energy of the occupant. The load of the seat belt can then be transferred to the occupant as a force caused by the seat belt. It is desirable to reduce the force incurred by the occupant.
To reduce the force, a variety of seat belt retractors with seat belt load limiting mechanism have been developed. The seat belt load limiting mechanism comprises a torsion bar and a shear pin as a shearing member which are disposed between a spool for winding up a seat belt and a locking plate for locking the rotation of the spool in the belt withdrawing direction.